Multiplex Control of Polymer Structure by Stereospecific Living Polymerization----Livingness, sterepspecificity, monomer-selectivity, and site selectivity

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Bulky aluminum phenoxide in combination with t-BuLi was found useful for the control of livingness, stereospecificity, and monomer selectivity in the polymerization and copolymerization of methacrylate, leading to the multiplex control of polymer structures.1) A combination of bis(2,6-di-t-butylphenoxy)methylaluminum [MeAl(ODBP)ィイD22ィエD2] and t-BuLi (Al/Li>2) gives heterotactic (ht-) polymers with narrow molecular weight distribution in the polymerization of several alkyl methacrylates in toluene at low temperature. In particular, the mr contents of polymers of ethyl(EMA), propyl and allyl methacrylates obtained at -95℃ were 92,94,96%, respectively.2) ht-Oligomer of ally methacrylate was prepared and separated into uniform oligomers by supercritical fluid chromatography (SFC) and their stereochemical structures were elucidated by 13C NMR, revealing that odd-number DP oligomers have higher stereoregularity than even-number DP oligomers at their chain ends.3) Copolymerization of EMA and … More TMSMA with t-BuLi/MeAl(ODBP)ィイD22ィエD2 at -78℃ gave a block copolymer comprising ht-poly (EMA) block and st-poly (methacrylic acid) block after hydrolysis. MeAl (ODBP)ィイD22ィエD2 presumably coordinates with the less bulky EMA preferentially and activates it to give the poly (EMA) block first, and the addition of TMSMA to the poly (EMA) anion occurs thereafter to give a poly (TMSMA) block. Copolymerization of EMA and t-butyl acrylate (t-BuA) at -60〜-30℃ also proceeds in a monomer-selective manner, where t-BuA is polymerized first, though the rate of homopolymerization of t-BuA is smaller than that of EMA. The polymerization process was minutely studied with the aid of on-line GPC/NMR analysis of the polymers formed.4) Several methacrylates having polar functional groups in the ester side chain such as tertiary amino group were found to give syndiotactic polymer instead of ht-polymer, probably due to specific interaction of MeAl (ODBP)ィイD22ィエD2 with the functional groups.5) Use of EtAl (ODBP)ィイD22ィエD2 in place of MeAl (ODBP)ィイD22ィエD2 allows living polymerization of primary alkyl acrylates and also provides monomer-selectivity in the copolymerization of acrylate and methacrylate such as butyl acrylate (n-BuA) and methyl methacrylate (MMA), where n-BuA polymerized preferentially to give block copolymer with low Tg segment of poly (n-BuA) and high Tg segment of st-PMMA.6) A dimethacrylate with primary and tertiary ester linkages was prepared and polymerized with t-BuLi/MeAl (ODBP)ィイD22ィエD2 where site-selective polymerization takes place to afford a soluble polymer with a pendant tertiary ester of methacrylate. Less